The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Compressors may be used in a wide variety of industrial and residential applications to circulate refrigerant within a refrigeration, heat pump, HVAC, or chiller system (generically “heat pump systems”) to provide a desired heating or cooling effect. In any of the foregoing applications, the compressor should provide consistent and efficient operation to ensure that the particular heat pump system functions properly.
Compressors may include crankcases to house moving parts of the compressor, such as a crankshaft. Crankcases may further include lubricant sumps, such as an oil reservoir. Lubricant sumps include lubricants that lubricate the moving parts of compressors. Lubrication of the moving parts may improve performance and/or prevent damage.
Lubricants in the crankcases may cool to low temperatures when the compressor is not running. For example, the crankcases may cool due to a low outdoor ambient temperature. Additionally, lubricants may cool and/or be diluted when liquid refrigerant returns to the compressor during the running cycle. Lubricant cooling may also occur under other circumstances.
Lubricant properties may change at low temperatures. More specifically, lubricants may become more viscous (i.e., thicker) at low temperatures. Starting a compressor with a low crankcase temperature and/or a significant amount of liquid within the shell may cause bearing wear and/or decreased performance due to insufficient lubrication.